This invention relates generally to manufacturing of medical instruments, and, more specifically, to the manufacture of a catheter electrode assembly for an impedance spectroscopy system.
Impedance spectroscopy has been used to detect ischemia (a condition of inadequate blood flow and oxygen delivery to a given tissue) in biological tissues using different instrumental methods. Impedance spectroscopy differs from other impedance measurements (which have long been used for a variety of biomedical applications) in that it involves multiple measurements over a range of frequencies that as a whole contain significantly more information of the structural and electrical properties of the sample.
At least one known impedance spectroscopy system for monitoring tissue damage in hollow viscous organs includes a sensor catheter and an impedance spectrometer for electrically driving the catheter to obtain a complex impedance spectrum of tissue proximate the catheter. The catheter is configured to be inserted into any hollow viscous organ, and the catheter includes four Ag/AgCl electrodes positioned on an end tip of the catheter. The electrodes are coaxially spaced apart a short distance from one another, and the outer two electrodes inject current into the tissue, while the inner two electrodes measure the resulting voltage. Leads, electrically connected to the electrodes, extend along the wall of the catheter tubing or in a lumen portion of the tubing, and terminate at an interface plug suitable for electrical and mechanical connection to the impedance spectrometer. Once the catheter is in place in one of a patient's hollow viscous organs, the impedance spectrometer causes the electrodes in the tip of the catheter to inject a current into the mucosal tissue at different frequencies, allowing for the measurement of the tissue's complex impedance spectrum. Analysis of the spectrum determines the extent to which the tissue is damaged. See. for example, U.S. Patent Application Publication US 2002/0013537.
The construction of the catheter tip assembly for such a system has proven difficult in a number of aspects. The catheter tip assembly is, for example, typically inserted into the throat or nasal passage of a patient and into a gastrointestinal organ, and the therefore must be of a relatively small size and have a uniform, high quality surface finish. The tip assembly, however, includes a relatively large number of component parts which must be assembled and interconnected, including a tip, four electrodes, dielectric spacer elements between the electrodes, and leads attached to each electrode, which can make a uniform surface finish difficult to achieve. Additionally, assembly of the many component parts is cumbersome, and separately connecting the electrical leads to the spaced electrodes in a reliable manner is difficult. Managing the wire leads in the constrained internal space of the assembly, which entails threading the wires through the dielectric spacer elements, is especially difficult. These and other difficulties not only complicate the tip assembly time and increase manufacturing costs, but may negatively affect the performance and reliability of the impedance spectroscopy system when treating critically ill patients.